Work will be performed to better characterize the sensitized T-cells that mediate active immunity to infection with the bacterial parasite Listeria monocytogenes. These protective T-cells will be examined to determine their Lyt phenotype with the view to discovering whether they are the same as the sensitized T-cells that mediated delayed-type hypersensitivity to Listeria antigens. Peritoneal inflammatory exudates will be employed as a concentrated source of protective T-cells, and purification achieved by adherence of macrophages on plastic surfaces and the destruction of B cells by anti-Ig serum and anti-Ia serum. The purified T-cells will be radiolabelled, and their fate followed after intravenous infusion into Listeria-infected recipients with the aim of discovering whether most of them home to foci of infection. The same purified T-cells will be studied to determine whether the number of protective T-cells can be greatly increased in vitro by incubation with Listeria antigens. Large numbers of such T-cells will be employed in an attempt to terminate chronic listerosis in athymic nude mice, and to determine again whether an anti-Listeria effect is associated with the accumulation of radiolabelled T-cells at foci of infection. Immunity to murine salmonellosis will be studied to determine the identity of the spleen cells in reinfected donors that can adoptively immunize normal recipients.